High and low pressure turbine parts including turbine vanes or airfoils are made of nickel based superalloys. These components are protected against the high temperature environment by a thermal barrier coating (TBC). In the TBC, a bond coat disposed in between the top oxide layer and the substrate superalloy provides an aluminum reservoir, which supply aluminum diffusing outwards to form protective α-Al2O3, an adherent thermally grown oxide (TGO). Thus, the bond coat is critical for protecting gas turbine components from high temperature oxidation. Like aluminum, chromium tends to form dense oxide chromia in a high temperature environment, providing hot corrosion protection. These elements allow the parts made from nickel alloys to perform well in gas turbine engines.
Turbine vanes are occasionally removed from service due to the loss of wall thickness during such repair processes as coating stripping, recoating, grit blast cleaning, and chemical processing which typically remove some base metal and often reduce component wall thicknesses below the required minimum thickness.
Thinned turbine vanes or airfoils are either replaced with new parts or scrapped unless the lost wall thickness is restored by adding metal materials that include key elements (e.g., Cr and Al) lost during the repair processes.
Accordingly, it is desirable to restore the lost wall thickness of turbine vanes or airfoils by providing a metal coating layer that includes key elements (e.g., Cr and Al) lost during the repair processes to increase the number of repair cycles for the vanes or airfoils.